The present invention relates to a method of using a chemical grout wherein water-soluble polymers are crosslinked with iron to form a gel for sealing sewer pipe joints, soil stabilization, water proofing, controlling water flows, and profile modification of oil field producing and injection wells. Additionally, it relates to a chemical grout that will not expose workers or the environment to toxic chemicals such as acrylamide, chromium, or aluminum.
The idea of using mixtures of acrylamide and N,N-methylenebisacrylamide in aqueous solutions for the stabilization of soil was developed in the early 1950's. Reference is made to the U.S. Pat. Nos. 2,801,983; 2,801,984; 2,801,985; 2,868,753; 2,940,729; 3,056,757; 3,136,360; and 3,223,163. The technology consists of mixing acrylamide and methylenebisacrylamide in water and pumping them with a catalyst in separate lines to the point of application where they are mixed and a polymerization reaction takes place forming a crosslinked polymer gel in water. The reaction time is controlled by catalyst concentration and retarder. A major disadvantage with this type of grout is that acrylamide monomer is toxic and is environmentally detrimental to the underground water supply and to workers.
The toxicity of acrylamide monomer was eliminated by crosslinking water-soluble acrylamide polymer with metal ion, such as chromium by taking the metal at its highest valence state Cr.sup.+6 and reducing it to Cr.sup.+3 which crosslinks the polymer The gel time is controlled by the polymer concentration, temperature, and the choice or reducing agent. Another method of profile modification consists of injecting a slug of polymer into the formation followed by a chelated trivalent metal ion such as aluminum citrate followed by another polymer slug. While this procedure yields a strong grout, it presents the problem of the toxicity of the chromium ion which is an unacceptable contaminant in ground water and hazardous to workers.
The fact that ferric ion will crosslink water-soluble polymers in well known. It is taught in U.S. Pat. Nos. 4,825,949; 4,039,029; 4,018,286; 3,785,437 and 3,762,474. In these patents, iron is claimed to be used with a chelating agent, in its highest oxidative state and reduced to its lower oxidative state to crosslink the polymer In fact, iron will successfully crosslink acrylamide polymer only in its highest oxidative state Fe.sup.+3 not the lowest Fe.sup.+2. Furthermore, the crosslinking of water-soluble, acrylamide polymers with iron has always been uncontrollable making it impossible to place the gels where they are needed thereby necessitating the exclusive use of chromium and aluminum for crosslinking these water-soluble polymers. According to the present invention, iron is added to the polymer solution in its reduced form Fe.sup.+2 such as ferrous chloride, ferrous ammonium sulfate etc. and in the presence of the polymer it is oxidized to ferric Fe.sup.30 3 ion which then crosslinks the polymer to form the gel. The reaction takes place at a pH of from about 2 to 9, but preferably between 3 and 7. The gel time is dependent, on the polymer concentration, the iron concentration, the temperature and the oxidizer. The amount of iron needed depends on the polymer used and the concentration of the polymer. Gels can be made using polyacrylamides, copolymers of acrylamide and acrylic acid, polyacrylates, modified cellulose polymers, polysaccharides, and copolymers of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid and the like.
The fast gel times that can be obtained by ferric ion crosslinking make it very well suited for subterranean profile modification.
It is therefore an object of this invention to provide an environmentally safe chemical grout that will not expose field workers to, nor contaminate ground water with, toxic monomers such as acrylamide monomer, or heavy metal ions such chromium Said grout is useful in sewer joint sealing, soil stabilization, water proofing and water flow control Furthermore, the grout is chemically stable and able to withstand contact with chemicals likely to be found in a sewer system such as acids, bases, oils, solvents, detergents and salts.